Three variables do most of the work: dose, grind, and time. Get these talking to each other and the rest follows.
Start from a known point. Pull an 18g dose toward a 36g cup in about 28 seconds and taste. Sour and thin means the shot ran too fast; grind finer. Harsh and bitter means it choked; grind coarser. Change one thing at a time and keep notes for the first week.
Freshness matters more than gear. A modest grinder with beans roasted days ago will beat an expensive setup running stale coffee. Once the shot tastes sweet and balanced, lock the grind and only nudge it as the bag ages.